1. Field of the Invention
The present invention relates to a fluorine-containing elastomer composition, and more particularly to a fluorine-containing elastomer composition capable of giving vulcanization products having a distinguished permeation resistance to fuel oil.
2. Related Prior Art
JP-A-8-12840 discloses a fluorine-containing elastomer composition having a good processability and for use as vulcanization molding materials for fuel hoses, injector O-rings, etc. The fluorine-containing elastomer composition comprises, as essential components, a fluorine-containing elastomer being a vinylidene fluoride-based copolymer or terpolymer containing at least 67% by weight of fluorine and comprising 30 to 50% by weight of vinylidene fluoride and 20 to 60% by weight of hexafluoropropylene, and an adduct of a polyhydroxy or polythiol compound curing agent and a quater-nary phosphonium salt compound promoter in a ratio of the curing agent to the promoter of 2 to 5 by mole.
It is further recommended that an aminophosphonium compound is preferable as a quaternary phosphonium salt compound as a promoter component. However, such an amino-phosphonium compound is very hard to obtain and also very expensive, giving a serious obstacle to the industrial utilization. Furthermore, it is not desirable to use an amine compound having a carcinogenic fear, and there is also a fear of generation of unpreferable nitroso compounds from the amine compound when used in the heat vulcanization.
It is known that a fluorine-containing elastomer having a high fluorine content generally has low in the gasoline permeability, and thus it is a highly desirable material in light of total discharge control of gasoline from automobiles (Carifornia SHED regulations, USA). Above all, a fluorine-containing elastomer having a fluorine content of 68% by weight, has a good balance between the permeation resistance to gasoline and the low temperature resistance. However, when a vinylidene fluoride-based copolymer or terpolymer containing vinylidene fluoride (VdF) and hexafluoropropylene (HFP) is cross-linked with a polyhydroxy compound, its cross-linking mechanism seems to be an addition reaction of phenolate anions onto the double bonds formed by dehydrofluorination reaction of VdF-HFP chains. The VdF-HFP-based copolymer or terpolymer having a high fluorine content has less VdF-HFP chains, and thus the cross-linking reaction by a polyhydroxy compound proceeds very slowly. Such tendency is remarkable particularly in case of fluorine-containing elastomer having a fluorine content of 68% by weight or more. Slow cross-linking reaction will lower a cross-linking density, further resulting in decrease in physical properties such as compression set, etc.